First, why is the asking of critical questions about "knowledge" and the "nature of the ultimately real" to be limited to the province of religion?
The history of Western philosophy testifies to a parallel tradition of perfectly respectable non-religious answers to such questions. Or is the Archbishop using the term "religion" to include these? If so, he is in danger of confusing the issue. Why not, alongside "religion", use the terms like "philosophy" or "metaphysics" if this is what is really meant?
Second, while lack of time and resources have certainly played a part in the quality of teaching in schools, a more salient factor is the narrow conception of the subject inherent in the syllabuses of the examination boards and the local education authorities themselves. These focus almost entirely on religion - religious writings, religious people, religious faith, religious places, religious experiences - and leave little room for any wider exploration of questions of knowledge and reality or the development of the skills of critical thinking.
If the Archbishop genuinely wishes to improve the quality of teaching in schools, perhaps the best place he could start is by broadening the conception of what should be taught - no longer RE but religion and philosophy? - and persuading the School Curriculum and Assessment Authority and the Department for Education to press the examination boards for more appropriate examination syllabuses. His Anglican co-religionists could perhaps do likewise with their local education authority colleagues.
Department of religion and philosophy